1.\" 2.\" Copyright (c) 2009 Sam Leffler, Errno Consulting 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 14.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24.\" SUCH DAMAGE. 25.\" 26.Dd August 4, 2009 27.Dt IEEE80211_BEACON 9 28.Os 29.Sh NAME 30.Nm ieee80211_beacon 31.Nd 802.11 beacon support 32.Sh SYNOPSIS 33.In net80211/ieee80211_var.h 34.Pp 35.Ft "struct mbuf *" 36.Fo ieee80211_beacon_alloc 37.Fa "struct ieee80211_node *" 38.Fa "struct ieee80211_beacon_offsets *" 39.Fc 40.\" 41.Ft int 42.Fo ieee80211_beacon_update 43.Fa "struct ieee80211_node *" 44.Fa "struct ieee80211_beacon_offsets *" 45.Fa "struct mbuf *" 46.Fa "int mcast" 47.Fc 48.\" 49.Ft void 50.Fn ieee80211_beacon_notify "struct ieee80211vap *" "int what" 51.Sh DESCRIPTION 52The 53.Nm net80211 54software layer provides a support framework for drivers that includes 55a template-based mechanism for dynamic update of beacon frames transmit 56in hostap, adhoc, and mesh operating modes. 57Drivers should use 58.Fn ieee80211_beacon_alloc 59to create an initial beacon frame. 60The 61.Vt ieee80211_beacon_offsets 62structure holds information about the beacon contents that is used 63to optimize updates done with 64.Fn ieee80211_beacon_update . 65.Pp 66Update calls should only be done when something changes that 67affects the contents of the beacon frame. 68When this happens the 69.Dv iv_update_beacon 70method is invoked and a driver-supplied routine must do the right thing. 71For devices that involve the host to transmit each 72beacon frame this work may be as simple as marking a bit in the 73.Vt ieee80211_beacon_offsets 74structure: 75.Bd -literal 76static void 77ath_beacon_update(struct ieee80211vap *vap, int item) 78{ 79 struct ieee80211_beacon_offsets *bo = &ATH_VAP(vap)->av_boff; 80 setbit(bo->bo_flags, item); 81} 82.Ed 83.Pp 84with the 85.Fn ieee80211_beacon_update 86call done before the next beacon is to be sent. 87.Pp 88Devices that off-load beacon generation may instead choose to use 89this callback to push updates immediately to the device. 90Exactly how that is accomplished is unspecified. 91One possibility is to update the beacon frame contents and extract 92the appropriate information element, but other scenarios are possible. 93.Sh MULTI-VAP BEACON SCHEDULING 94Drivers that support multiple vaps that can each beacon need to consider 95how to schedule beacon frames. 96There are two possibilities at the moment: 97.Em burst 98all beacons at TBTT or 99.Em stagger beacons 100over the beacon interval. 101Bursting beacon frames may result in aperiodic delivery that can affect 102power save operation of associated stations. 103Applying some jitter (e.g. by randomly ordering burst frames) may be 104sufficient to combat this and typically this is not an issue unless 105stations are using aggressive power save techniques 106such as U-APSD (sometimes employed by VoIP phones). 107Staggering frames requires more interrupts and device support that 108may not be available. 109Staggering beacon frames is usually superior to bursting frames, up to 110about eight vaps, at which point the overhead becomes significant and 111the channel becomes noticeably busy anyway. 112.Sh SEE ALSO 113.Xr ieee80211 9 114